Half-hardy annuals

Grow the border’s tarty barmaids from seed

The big show-stoppers in the annual garden are, more often than not, half-hardy types, like these lovely Cosmos.

Mandy’s own white Cosmos Cupcakes, July 2015

Cosmos bed at Harlow Carr

Cosmos Cupcakes and scented geraniums

Sometimes they’re tender perennials, like dahlias – you can usually spot them, as they’re the ones being sold as plug plants in catalogues and garden centres, costing a small fortune.

They all need a long season to flower well, which necessitates indoor sowing in a propagator sometimes as early as January (Antirrhinums), but more usually February/March.

What is critical here is light intensity. If you don’t have a brightly-lit place indoors, wait until March. Warmth and poor light will lead to leggy, weak seedlings which will easily fall victim to disease.

Propagator’s a good buy

A propagator with a constant temperature is a good buy too. Bear in mind how much plug plants cost, and it will soon pay for itself.

What they all need is good seed compost – buy the best you can afford. Some people like to cover seeds with Vermiculite or Perlite instead of compost – use what you know best. (I find the latter two don’t form a crust which is hard to wet, which is why I use them).

Make sure the soil is watered before you sow and doesn’t dry out. Sealing trays/pots in cheap freezer bags works well.

There’s a lot of old bedding favourites here – this is a quick guide to their germination temperatures; sowing depth; days to germination; and any special instructions.

Single not double dahlias

I’m not really a fan of the big show dahlias, but I do love the simpler, single types, such as Bishop of Llandaff, with its dark foliage and striking red flowers – ideal for a sunny, hot-themed border.

Dahlia Bishop’s Children pink form, which I grew from seed

Dahlia Bishop’s Children orange form, which I grew from seed

Dahlia Bishops Children

Bees and insects can’t get to the nectar in double flowers – another reason to grow singles.

You can buy tubers, but if you like a riot of colour and growing from seed, try Bishops Children (I bet the Church wasn’t happy about that name).

They are half-hardy perennials but are usually grown as annuals. You can lift the tubers in autumn for next year. I did this – they do survive well in a frost-free place.

They need a long growing season, hence the early sowing, but will flower until the first frosts.

Sow 0.6cm deep in trays and cover with compost, Vermiculite or Perlite. They should germinate in 7-21 days – don’t exclude light.

My packet cost £2.49 (40+ seeds) – the cheapest Bishop of Llandaff SINGLE tuber I could find was £3.25, ranging up to £9.99 for a potted plant.

Antirrhinums from seed

Cottage garden favourites Antirrhinums or snapdragons, are a half-hardy perennial but are best grown as an annual – which means an early start.

Sow seeds January-March, thinly, in trays of seed compost.

Don’t cover the seeds, or exclude light, as this helps germination. Keep moist and maintain a temperature of 18-22°C (64-72°F). Germination should take 10-29 days but may be erratic.

The seedlings are tiny – don’t be put off if they seem to be making little progress – I always think they’re going to die young.

Antirrhinum Tootsie

Antirrhinum The Bride

Antirrhinum Purple Twist

Seeds can be sown July-September in a cold frame for planting out the following spring, but that’s too nerve-wracking for me.

When they are large enough to prick out, transplant them 5cm apart in seed trays ( or I use small modules) and grow on. Gradually acclimatise the plants to outside conditions before planting out 12-25cm apart (depending on the size of the variety) in a sunny position.

Potted guide: Antirrhinums

Sow: January-March or July-Sept.

Flowering: June-October.

Position: full sun.

Hardiness: Although half-hardy perennial, treat as a half-hardy annual.

Archives

Subscribe to Blog via Email

Mandy Watson is a freelance journalist and an incurable plantaholic. MandyCanUDigIt grew from the tiny seed of a Twitter account into the rainforest of information you see now. Gardening columnist (Sunderland Echo, Shields Gazette, Hartlepool Mail), Teesdale Mercury Magazine editor. Attracted by the rebellious, exotic and nerdy. Passionate about northern England and gardens everywhere. Falls over a lot.